Aircraft engines normally have double accessories for each necessary function of the engine. For example, an aircraft internal combustion piston driven engine usually includes two ignition systems, two carburetors, two generators, two fuel pumps, etc. Similarly, turbine engines, such as those used for turboprop on jet propulsion, include duplicate accessory units continuously driven by the engine, such as electric alternators or generators, vacuum pumps, hydraulic pumps and the like. Normally only one of the two units is used to operate the engine, but an auxiliary unit is essential if a primary accessory unit fails in flight. Accordingly, it is the practice of industry to drive both the primary and auxiliary units at the same time. Such full time operation of both units frequently results in the auxiliary unit being worn out or broken (since it runs just as long as the primary unit) just when it is most needed.
It has been proposed, as in U.S. Pat. No. 4,167,695--Phillips to provide a decoupling arrangement to disconnect an aircraft engine electrical generator if the unit fails mechanically or electrically in flight. The patent discloses a specially constructed drive shaft which is mechanically disengageable by an electric latching solenoid. Such construction requires replacement of a conventional generator with a unit having a larger diameter shaft internal to the generator rotor. Such space is frequently not available and replacement of such special units would limit interchangeability for replacement by a spare part, and the like. Further, no means for selective immediate remote engagement and disengagement of the auxiliary unit during operation is available.
Electrical systems for transferring load between two separate operative electrical power systems are known as shown in U.S. Pat. No. 3,249,769--Mierendorf, U.S. Pat. No. 3,265,987--Hahnel, U.S. patent Reinert, et al., and U.S. Pat. No. 3,723,750--Dixon, et al. However, none of these contemplate a compact clutch mounting means for selectively engaging or disengaging a friction clutch to operate stand-by or auxiliary aircraft engine accessory power equipment upon demand. Further, none of the prior art discloses a concept of making available to an aircraft pilot, during flight, the ability to engage any of several standard accessories needed for continued operation of an engine, with reasonable assurance that such accessory is not broken or worn out by continuous drive of the unit by the engine, whether or not in use. Additionally, little or no modification of the limited space available on the aircraft engine, or its mounting within a nacelle, is required by the compactness of the mounting clutch, and no modification of a standard accessory for such an engine is required to so mount it on the mounting clutch.
Further, it is now common practice, particularly in single engine aircraft, to provide the engine with two or more standard mounting pads, designated as A.N.D. 20000, for mounting auxiliary or stand-by accessories. In this way an auxiliary generator and an auxiliary vacuum or air pump are mounted for direct drive by the engine at the same time that the engine is driving the main engine generator, pumps, etc. Where such mounting pads are standard, the engine nacelle is normally configured to permit the auxiliary units to be installed or replaced without modification or disassembly of other parts of the aircraft or engine.